(1) Field of the Invention
The present invention generally relates to a data transmission processing system, and more particularly to a data transmission processing system for executing a data transmission process in a DMA (Direct Memory Access) transmission mode between a host unit and peripheral device.
(2) Description of Related Art
In facsimile machines, for example, a host unit 11 and a laser printer 1 are coupled to each other via a hand-shake logic (hereinafter HSL) unit 2 as shown in FIG. 1. The laser printer 1 is provided with a slave CPU (Central Processing Unit) 3 and a PROM (Programable Read Only Memory) 4 that are used for the data transmission process in the DMA transmission mode, as shown in FIG. 2. The PROM 4 stores a DMA processing program for the DMA transmission mode. The CPU 3 controls the data transmission process in the DMA transmission mode in accordance with the DMA processing program stored in the PROM 4. The printer 1 is also provided with a page memory 5 formed of a DRAM (Dynamic Random Access Memory), a laser diode synchronous unit (hereinafter referred to as an LDS unit) 6, an SRAM (Static Random Access Memory) 7 and a laser driver 8 for driving a laser diode 9.
Image data supplied from the host unit 11 via the HSL unit 2 is transmitted to the page memory 5 in the DMA transmission mode. The image data is further transmitted from the page memory 5 to the LDS unit 6 in the DMA transmission mode. The SRAM 7 modifies addresses of image data to perform a smoothing process for the image data. The LDS unit 6 supplies the image data processed by the SRAM 7 to the laser driver 8 in synchronism with the operation of the laser driver. The laser driver 8 drives the laser diode 9 based on the image data supplied from the LDS unit 6 during a predetermined scanning time. A laser beam emitted from the laser diode 9 driven by the laser driver 8 is projected onto a photosensitive drum, so that an electrostatic latent image corresponding to the image data is formed on the photosensitive drum. A detector unit 10 detects an end position of one scanned line of the laser beam and outputs a LNSYNC signal representing one scanning line. The LNSYNC signal is supplied from the detector unit 10 to the laser driver 8.
In the data transmission process in the DMA transmission mode controlled by the slave CPU 3, the image data read by a scanner in the host unit 11 line by line is transmitted to the laser printer 1 via the HSL unit 2, and is stored in the page memory 5 line by line while an address is being incremented one by one from a starting address. In a case where image data is transmitted from the page memory 5 to the LDS unit 6 in the DMA transmission mode, image data of pixels within a matrix lying over a plurality of lines, the matrix comprising an attentional pixel and peripheral pixels surrounding the attentional pixel, is transmitted from the page memory 5 to the LDS 6 in the DMA transmission mode by a single process.
According to the width of a document (e.g. A4 size, B4 size or the like) read by scanner in the host unit 11, the length of each address area for one line is changed in the page memory 5. As the image data of pixels in the matrix, which matrix lies over a plurality of the lines, is transmitted from the page memory 5 to the LDS unit 6 in the DMA transmission mode by a single process, read addresses of the image data of pixels in the matrix are skipped. The image data of the pixels is temporally stored in the SRAM 7 so that the skipped addresses of the image data of the pixels in the matrix are modified, and the image data of pixels is then supplied to the laser driver 8.
In the above conventional data transmission system provided in the laser printer 1 in which system the smoothing process for the image data is performed, the SRAM 7 is needed to modify addresses of image data of pixels in the matrix. As a result, the control of the data transmission in the DMA transmission mode between the page memory 5 and the LDS unit 6 is complex. In addition, the slave CPU 3 and the PROM 4 are needed for performing the data transmission process in the DMA transmission mode. Thus, the number of parts in a circuit for the data transmission process in the DMA transmission mode is large, so that a high cost is required to producet the laser printer 1.